In a variety of applications there is a need to authenticate the identity of a user before he can use a certain service, or gain access to a restricted data or a physical location. A common approach to address this need is by using computerized biometric verification techniques. According to this two steps approach, the first step is known as “enrollment” where an identifiable and preferably unique set of biometric characteristics of a person are being extracted to generate a “template” aimed to function as a biometric signature of that person. The template is then being stored in a centralized data base. In the second step (usually at a distinct occasion and can be repeated for many times), the same biometric characteristics are being extracted to generate yet another template which is compared to the first template. If there is a high degree of match between the parameters in the two templates beyond a certain threshold, the person is authenticated in the biometrical sense. In the known art, there are variety of methods to implement this approach which are based oil different biometrical attributes (also known as modalities) such as human face, iris, voice, finger print, hand geometry and others. It is also possible to combine several of these modalities to create a multimodal solution e.g. using both face and finger print parameters.
While the biometric approach for authentication is gaining an increasing popularity, there are some barriers for a massive use of it in many applications. Two of these barriers are:                1) The need for the “enrollment” step, where in this step the user identity is needed to be determined by his/her physical attendance at some specific location, where he/her can show an identifier (e.g. an identity card). Then, one needs to go through the enrollment process which can be a time consuming and expensive process.        2) Storing user's biometric data in some organization's centralized database generates a real privacy problem, and is even currently illegal in some places. In addition, in some cases it is prohibitive to use persistent data. An alternative approach to central storing is to store the information on a personal “smart card”, which is being kept within the user possession. While this alternative reduces the extent privacy problem it is cumbersome, not practical and too expensive for many applications.        
In many cases, biometric verification is often used only as a complementary mean to other simpler authentication methods like the use of password. Many web sites use only password to assure that the person logged in is indeed the legitimate person and not an imposer. It has been demonstrated that adding a biometric check in addition to password, reduces abuses significantly.